1. Technical Field
The present invention relates to a stepping motor control circuit configured to drive a stepping motor by selecting an adequate drive pulse from among a plurality of drive pulses, a movement provided with the above-described stepping motor control circuit, and an analogue electronic timepiece using the above-described movement.
2. Description of the Related Art
In the related art, an analogue electronic timepiece in which a stepping motor is configured to driven to rotate by selecting an adequate drive pulse according to the condition of the rotation of the above-described stepping motor has been developed.
For example, in the invention described in International Publication No. 2005/119377, there is provided a unit configured to compare and discriminate a time of day when an induced signal VRs generated by the rotation of the stepping motor is detected with and from a reference time when the stepping motor is driven to rotate at a main drive pulse Pl. Every time when the stepping motor is driven to rotate at the main drive pulse P1, the counted value of a counter is incremented by one if the time of day when the induced signal VRs is detected is earlier than the reference time, and the main drive pulse P1 is pulsed down to a main drive pulse P1 having energy one rank lower when the above-described counted value becomes a certain value, whereby the consumption current may be reduced.
However, the internal resistance of a cell used as a power supply of the analogue electronic timepiece has a property of rising abruptly in a low-temperature environment in comparison with a normal-temperature environment. In such a case, a detected cell voltage may be different significantly from a voltage actually applied to the stepping motor.
Even with a main drive pulse P1 which is sufficient for rotating the stepping motor when the cell voltage is equal to a voltage (motor voltage) applied to the stepping motor, if the the cell voltage is larger than the motor voltage, drive energy shortage may result. In such a case, the main drive pulse P1 is not capable of rotating the stepping motor, which may result in slow movement of hands of the timepiece.
In contrast, in Japanese Patent No. 3407887, there is disclosed an electronic timepiece which achieves low power consumption by creating a plurality of drive pulse groups having main drive pulses P1 of different combinations and driving a motor by selecting a drive pulse group according to an output voltage of a power supply unit.
Application of the invention described in Japanese Patent No. 3407887 is contemplated in order to solve the above-described problem, but since the invention described in Japanese Patent No. 3407887 is intended to achieve low power consumption, when one of the drive pulse groups is selected, a drive pulse having the smallest energy in the selected drive pulse group is firstly used for driving. Therefore, when the cell voltage is significantly lowered as in a case where a cell whose cell voltage varies is used, the energy of the drive pulse may run short, and hence difficulty of driving may result.